5 Free STL Editors + How to Edit STL Files

How do I edit STL files? That is something any 3D printer owner sooner or later wonders. After all: Ready-made STL files are fine. But what if an STL file you downloaded lacks some features, is damaged or you need only a part from it? That’s when you need an STL editor. We show you how to edit an STL file with 5 free STL editors: FreeCAD, SketchUp, Blender, Meshmixer and Meshlab.

Editing STL files can be done in two different types of modeling software:

On the one hand, there is CAD software (Computer Aided Design), which is designed for construction, exact measurements and solid modeling. These tools were not made for 3D printing in the first place. In CAD software, circles for example are “real” circles; in 3D printing – and in STL files for 3D printing – circles are represented as polygons. So CAD tools cannot show their full strength when editing STL files, nevertheless, they can be used for working with STL files. Three of the four tools we present in ths article are true CAD tools: FreeCAD, SketchUp and Blender.

On the other hand, there are mesh editing tools such as MeshMixer and MeshLab that are designed for modeling, animation, and objects represented by a 2D surface. That means: These objects have just a shell and no filling. This may cause paper-thin walls in 3D printing, which can result in troubles, if the object is not solidified (which, however, can easily be done in tools such as Meshmixer). In fact, mesh editors are excellent tools when it comes to editing STL files.

Free STL Editors: Overview

Free STL Editor #1: FreeCAD

FreeCAD is an open source and free to use CAD software. It offers many different tools for construction, like Drafts, Drawings and Design features. You can download FreeCAD for free from the FreeCAD project website. Simply select the correct version for your OS and install.

A serious limitation: FreeCAD has some problems with intercepting structures and may mess up the mesh, when it contains intercepting edges!

Step 1: Open STL file and convert it to solid model

Open FreeCAD and create a new document by clicking on File > New.

Click File > Import and select the object you want to modify. FreeCAD can open other mesh formats such as OBJ and AST as well.

Change your workbench to Part.

Change your workbench to Part.

Select the imported object in the Model window.

This useful tool will create a solid object out of many dots.

Now click on Part > Create shape from mesh. This will split up the imported object into many small triangles. You can adjust the precision of tessellation, but 0.10 is perfectly fine for most objects. If the number gets smaller, it will take longer to convert the object.

You can now delete or hide the imported mesh. This will show you the shape of your imported object consisting of many triangles.

Check Solid from shell and also select one face of your object. Then click the Create button.

Click Advanced utility to create shapes and select Solid from shell. Now click on any triangle forming your imported object and then on Create. You will not notice anything because the shape is overlapping the solid. Click Close to finish.

Next, delete or hide the old shape. You now have a solid object of your mesh file ready for editing.

Step 2: Edit STL file

Switch your workbench to Part Design.

Click on any face you want to add or remove material, so it shines green.

Now click Create Sketch.

First select one plane of your object then click Create Sketch.

Create a shape you want to extrude or cut into using the tools for drawing a circle, rectangle or lines.

Click on Close to confirm the sketch. If you want to edit the sketch, double-click it in the model tree.

Use Pad to extrude and Pocket to cut.

Now select a feature you want to apply. You can use the Pad tool to extrude or the Pocket tool to cut elements.

Step 3: Export as STL file again

To export your object as an STL file again, select the last feature in the model tree. Then click on File> Export and select Mesh formats.

The pros and cons of using FreeCAD

When using FreeCAD as an STL editor you really notice its purpose. It is a CAD program to create exact and models for mechanical use not for modeling. This is great when you want to construct technical objects. Sculpting a model in FreeCAD is very difficult; as FreeCAD lacks a free move-around 3D view, sculpting is nearly impossible.

Free STL Editor #2: SketchUp

SketchUp – formerly Google SketchUp – is a full-blown 3D modeling software that is now owned by architectural company Trimble Buildings. SketchUp is available as a commercial version called SketchUp Pro and as the free SketchUp Make edition. By installing different plugins you can adjust SketchUp up to your personal preference. You can download the free SketchUpMake edition from their official website.

Step 1: Install the STL plugin in SketchUp

To import STL files in SketchUp Make you need to install a plugin first (this plugin is already installed in the Pro edition).

Start SketchUp and click on Window > Extension Warehouse.

Now log in with your Google account.

Search for SketchUp STL. Select it and click install.

The SketchUp STL Plugin created by the SketchUp Team.

Step 2: Open STL file

When you have the plugin installed go to File > Import… and set the file type to STL files. Browse for the object you want to open and import it.

Step 3: Edit STL file

Use the Eraser to remove the edges of the triangles so you end up with a rectangle to extrude. You can also use the pencil or one of its shapes to create new sketches to extrude.

When you have created new sketches you can use the Push/Pull feature to extrude or cut through the model.

Pull to extrude and Push with your mouse to cut.

Use the Move tool to drag edges or vertices.

You can create a reference line by orbiting over a point or surface and then move to the actual point where you want to start or end.

Step 3: Export as STL file again

The pros and cons of using SketchUp

SketchUp is easy to use, runs smoothly and has all the tools to create a 3D model. However, it is missing some key features of an STL editor for example for creating a solid object or for translating the triangle mesh of an STL file to squares which are easier to edit.

Free STL Editor #3: Blender

Blender is a another great free program to either create models for printing, games or video clips. It contains many useful tools for example various algorithms for smoothening or interpreting a surface. It is also very easy to import and prepare STL files for modelling. However it will take some time to getting used to Blender, and due to its huge amount of different tools and commands it can be quite obscure. It also requires a powerful PC to display some models, especially if you subdivide the model in many smaller tiles.

Step 3: Export STL file

To export your object go to File > Export > .Stl.

The pros and cons of using Blender

Blender is a great STL editor, if you want to create high poly models. It offers many tools to sculpt and work out fine details in models. However, it takes a while to getting used to working with Blender and as already said: When having a high poly object, it will require a lot of computing power.

Step 1: Open STL file

To import an STL file simply click on Import and browse for your object.

Make your object solid. Alternatively, you can make it hollow.

Click on Edit > Make solid.

Step 2: Edit STL file

You can now use Select to mark parts of your model.

Press Del to remove marked tiles.

Use Meshmix to open different forms.
Insert different forms and combine them with the Sculpt tool.

You can access more models by switching from basic forms to for example arms or legs. Drag and drop the object you want to insert. Use the different colored arrows to move or rotate to model. Use the little square in the middle of the arrows to scale the model.

Click on Sculpt to either smoothen or extrude different regions of the model.

Step 3: Export as an STL file

The pros and cons of using MeshMixer

MeshMixer is one of the best tools to edit your STL files. It takes all occurring problems like the paper-thin walls into account. Working with MeshMixer as an STL editor is easy and useful, if you just want to resize your model or change something.

Step 1: Open STL file

To open a supported mesh file go to File > Import Mesh and browse for your model.

Step 2: Edit STL file

MeshLab does not have the tools to create new vertices or objects. However, it is a great tool to combine two meshes of a 3D scan. You can also remove parts of the mesh and repair holes in the model.

In the Task bar you can find many useful tools.

How to merge two meshes:

To combine two meshes load both models.

Click on Show Layers. Select the models in the scene.

To transform, rotate or scale an object, first select it in the Layer menu and then click on Manipulator Tools.

You can now press T to select the Transform option, R to rotate the model and S to start scaling.

The direction you are looking at the model determines the coordiate system you are working in. Simply drag and drop the arrows to move or scale the model in one direction. Turn the circle around the object in order to rotate it. When you want to rotate your view, press Escape, and when you have the desired view on the object press Escape again to continue transforming. Press Enter to confirm the placement.

Use Flatten Visible Layers to merge two objects.

When you have put all the parts in place, right-click on any part of your combined mesh and click on Flatten Visible Layers. Check the first three boxes and click on Apply.

How to delete a section of a model:

To delete a part of the mesh click on Select Face in a rectangular region.

Then click Delete the Current Selected Face and Vertices.

How to repair your object or search for holes:

Click on Fill Hole. You model has to be manifold for this option.

A window will pop up and show you all the holes in the model. You can now select the holes you want to fill. They will shine green when selected. Click on Fill and then on Accept to finish.

Step 3: Export as STL file again

To export the model go to File > Export Mesh.

The pros and cons of using MeshLab

Even if MeshLab does not offer the option to create new objects, it is a great STL editor to combine or repair a mesh. Using MeshLab is a great and easy way to combine the mesh of a 3D scan or just to create new models by merging them.